Method and apparatus for communicating control and other information over a power bus

ABSTRACT

An information signal to be communicated to a roof-mounted light bar or other electrical or electronic device travels over the vehicle&#39;s or other environment&#39;s power bus or other power conductor. In one exemplary illustrative non-limiting implementation, a modulated current load draws power supply current in an amount that is instantaneously responsive to at least some characteristic of the information signal to be communicated. This modulated current loading induces the vehicular or other power supply (e.g., DC battery) to modulate its output voltage in a manner that is responsive to the modulated current loading. A voltage sensor and demodulator also connected to the power bus senses the resulting voltage fluctuations and demodulates those fluctuations to recover or regenerate the original information signal. The recovered information signal may be used for any purpose including but not limited to controlling aspects of the operation of an emergency vehicle light bar or other audible and/or visual warning system or other device. The data sender and data receiver can be co-located to provide a full duplex or half duplex powerline communicated transceiver.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of application Ser. No. 11/060,590, filedFeb. 18, 2005, now U.S. Pat. No. ______, the entire contents of whichare hereby incorporated by reference in this application.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD

The technology herein relates to communicating information-bearingsignals such as control signals over the power bus of a vehicle or otherenvironment, and more particularly to modulating a current load with theinformation signal to induce a mirrored voltage modulation. Exampleapplications include controlling devices including, but not limited to,emergency response lighting and/or sound-based warning systems such as,for example, police and other emergency response vehicle light bars.

BACKGROUND AND SUMMARY

We count on our police, firefighting and emergency medical responseteams every day. Ambulance and fire department emergency response teamssave countless lives and prevent property damage. Emergency responseteams are able to help because of their skills, their training and theirequipment. In the highly demanding world of front line police officers,fire fighters and emergency medical technicians, emergency equipmentmust work every time with practically 100% reliability.

Operating an emergency vehicle is one of the most common functionsperformed by today's fire and emergency service organizations. Yet, itis also one of the most dangerous. Collisions involving emergencyvehicles and personal vehicles injure many people each year. Effectiveemergency response vehicle warning systems such as rooftop-mounted lightbars, sirens, and the like, allow emergency response personnel torespond more effectively and safely. Manufacturers of emergency responsevehicle equipment such as emergency warning lights, light bars, sirens,and the like, have spent considerable time and effort developingeffective systems for warning of oncoming emergency response vehicles somotorists and pedestrians can get out of the way. Municipalities andgovernmental entities spend many millions of dollars each year to equiptheir emergency response teams with the most reliable, most effectivewarning systems available.

FIG. 1 shows an example of a marked or unmarked emergency responsevehicle 10, including a conventionally wired light bar 12 on its roof 14and conventionally wired grill and trunk accessories. Light bar 12 is aconventionally-designed light bar of the type most of us have seen onpolice cruisers, fire department vehicles, ambulances, tow trucks,emergency medical personnel vehicles, and the like. Light bar 12 can,for example, include conventional features such as for example low levelflashers, strobe lights, rotating lights, illumination lights, speakeror other audible warning indicators, sweeping intersection lights, etc.One example is the MX 7000 manufactured by CODE 3 of St. Louis Mo. See,for example, U.S. Pat. Nos. 6,595,669; 6,585,399; 6,582,112; 6,461,022;6,140,918; 6,081,191; D492,047; D489,466; D476,253; D460,950; D442,106;D427,537 and D410,402; and U.S. Patent Publication Nos. 2003/0007356,2003/0012032 and 2005/0007784. Additional light and/or warning systemsinstalled on-board the vehicle include grill mounted flashers, strobesor the like 16, trunk-mounted flashers, strobes or the like 18 and aconventional console-mounted switch box controller 20

Automobile manufacturers such as Ford, General Motors, Chrysler andothers typically manufacture special “police interceptor” versions ofstandard passenger vehicles. Such police interceptors often provide morepowerful engines and alternators, heavy duty suspension and frame,spotlights, and other special features. One option sometimes provided isa light bar connector for providing power to a roof-mounted light bar,which consists of a power cable coming directly from the vehiclebattery, which is left unterminated between the headliner and vehicleroof. However, such manufacturers typically do not ship emergencyresponse vehicles with light bars already installed. Instead,oftentimes, the purchasing governmental entity (e.g., local policedepartment, fire department, etc.) may install (or contract forinstallation of) such special equipment as required by particularemergency response personnel. Different police departments may makedifferent choices concerning manufacture and type of light bar, siren,and other special emergency response equipment. In general, suchequipment is not necessarily installed at the automobile manufacturer'sfactory, but rather is often installed later as part of an after-marketvehicle customization process. Such customization can end up beingexpensive and time consuming because of the additional wiring and othervehicle customization that may be required.

As shown in prior art FIG. 1, one prior art approach to controllinglight bars and other auxiliary equipment was generally to run anextensive set of multi-conductor cabling throughout the vehicle from aswitch box controller (e.g., of the type shown in FIG. 1A) to the deviceor devices being controlled. The FIG. 1A exemplary prior art switch boxcontroller 20 in this exemplary illustration includes a heavy single (12V) or dual (+12V, ground) power input connection (e.g., heavy gauge suchas AWG #4, #6, or #8) from the vehicle battery 22. Switch box controller20 switches the incoming vehicle battery power connection via variousswitches including, for example, a slider switch 24, also known as aprogressive switch, and rocker-type ON/OFF switches 26 as isconventionally known.

The exemplary illustrative prior art FIGS. 1 & 1A switch box controller20 outputs its switched power outputs through a multi-conductor cablebundle 28 having a separate conductor for each of the various devicesbeing controlled. For example, a conductor output by the switchboxcontroller 20 might be used to control the light bar 12 rotators,another output might be used to control light bar 12 alternatingflashers, still other conductors might be used to control left and rightalley lights, take down lights, a Priority Green optical preemptionemitter, etc. Typically, multiconductor cable 28 may comprise a13-conductor (or more) thick cable with ground.

While this design is highly reliable and has worked well for a number ofyears, it has the disadvantage that the resulting multi-conductor bundleof cables must be routed throughout the vehicle to the devices beingcontrolled. FIG. 2 shows one example of what can be involved ininstalling conventional light bars and associated control equipment in astandard conventional police interceptor-type vehicle. Generally, it istypically necessary for the after-market installer to run amulti-conductor wiring harness from the control interface unit on theconsole or dashboard through the vehicle in between the headliner andinside of the vehicle roof to the light bar. As FIG. 2 illustrates, thismay involve an extensive amount of disassembly of the vehicle including,but not limited to, removal of seats, dashboard portions and the like.All of these operations are time consuming and therefore are not onlyexpensive but may delay operational use of the vehicle by emergencyresponse personnel. Such cable routing can be costly due to the need toconceal the cables within headliners and other interior portions of thevehicle. Such installation may require a number of hours of work by askilled technician. It is not unusual for initial installation effortsto be unsuccessful, requiring the partial or entiredisassembly/reassembly process to be repeated in order to relievecrimped cables, bad connections, cosmetic bumps and blemishes, etc. Ifsuch wiring fails after installation, the same sort of disassemblyprocess may be required to repair or replace the wiring harness. Thiscan result in downtime during which the vehicle cannot be used. The sametype of extensive customization process may be required for otheremergency type vehicles such as tow trucks, volunteer fire departmentvehicles, emergency medical vehicles and the like.

It would be desirable to provide a more easily installed yet highlyreliable communications link to allow the user control interface withinthe vehicle to communicate information signals to the light bar withoutthe need to run additional wiring.

The technology herein provides a way to use power wiring to a light baror other device for delivering power from an automobile battery or otherpower supply as a path for communicating information such as controlsignaling.

In one exemplary illustrative non-limiting implementation shown in FIG.3, an information signal to be communicated to a roof-mounted light baror other electrical or electronic device travels over the vehicle's orother environment's power bus or other power conductor. In one exemplaryillustrative non-limiting implementation, a modulated current load drawspower supply current in an amount that is instantaneously responsive toat least some characteristic of the information signal to becommunicated. This modulated current loading induces the vehicular orother power supply (e.g., DC battery) to modulate its output voltage ina manner that is responsive to the modulated current loading. A voltagesensor and demodulator also connected to the power bus senses theresulting voltage fluctuations and demodulates those fluctuations torecover or regenerate the original information signal. The recoveredinformation signal may be used for any purpose including, but notlimited to, controlling aspects of the operation of an emergency vehiclelight bar or other audible and/or visual warning system or other device.The data sender and data receiver can be co-located to provide a fullduplex or half duplex powerline communicated transceiver.

Those skilled in the art understand that one of the challenges tocommunicating signaling within a vehicle relates to the substantialamount of electrical noise the vehicle generates. Alternators, heaterfan motors, ignition systems and light bar rotators all typicallygenerate substantial amounts of noise that can interfere with signalcommunications from one point within a vehicle to another.Communications techniques provided by the illustrative non-limitingexemplary implementations described herein are able to communicatesignals effectively and reliably over the main power bus used to supplypower to all systems on board the vehicle. In accordance with oneexemplary illustrative non-limiting alternate implementation, additionalswitches are provided to synchronously or asynchronously disconnectnoisy vehicle loads from the power bus from time to time (e.g., duringdata transmissions) in order to reduce the amount of noise the voltagesensor/demodulator sees. Such additional techniques may be helpful insome circumstances to achieve better performance.

In accordance with an additional exemplary illustrative non-limitingimplementation, a finite power-based powerline communications methodcomprises a transmitting method/arrangement and a receivingmethod/arrangement that can be used separately and/or together. Thepowerline transmitter makes use of the inability of a given power supply(e.g., a vehicle's 12 volt battery) to provide a completely voltageregulated output under a modulated current induced load, such that thepower supply is power-reactive to said load. The operation of thetransmitter produces a corresponding voltage mirror of the inducedcurrent modulation throughout the electrical system. To improvereception, a receiver located on the power line may increase thesignal-to-noise ratio by momentarily removing some or all current-drawnloads and thus increasing the line impedance such that the filtering toextract a given transmitter signal is decreased while signal integrityis increased.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better and morecompletely understood by referring to the following detailed descriptionof exemplary non-limiting illustrative embodiments in conjunction withthe drawings of which:

FIG. 1 shows an exemplary prior art emergency vehicle with conventionallight bar controlled with a conventional multiconductor power cable;

FIG. 1A shows a conventional exemplary prior art control switch andpower distribution switch box controller;

FIG. 2 shows the exemplary prior art emergency vehicle of FIG. 1 in astate that is disassembled to allow an installer to install theconventional light bar, multiconductor wiring harness and switch boxcontroller;

FIG. 3 shows an exemplary illustrative non-limiting implementation ofthe technology herein in a police vehicle including a roof-mounted lightbar;

FIG. 4 illustrates the basic electrical relationship between themodulated current load and the battery, and between the battery and thereceiver of the exemplary powerline communications system implementationof FIG. 3;

FIG. 5 is a more detailed block diagram of the exemplary implementationof FIG. 3;

FIG. 6 is a block diagram of an additional exemplary implementation ofthe FIG. 3 system including an interruption feature to decrease noise;

FIG. 7 is a schematic diagram of an exemplary illustrative non-limitingimplementation of a modulated load;

FIG. 8A is a schematic diagram of an exemplary illustrative non-limitingsignal capture and demodulation implementation;

FIG. 8B is a schematic diagram of an exemplary illustrative non-limitinglight bar controller implementation;

FIG. 9 is a flowchart of example program control steps for an exemplaryillustrative non-limiting pulse width modulated load;

FIG. 10 is a flowchart of example program control steps for an exemplaryillustrative non-limiting pulse width modulated receiver and controller;and

FIG. 11 represents exemplary electrical signals present in the variousillustrative non-limiting implementations described herein.

DETAILED DESCRIPTION

FIG. 3 shows an example police vehicle using the current modulated loadcommunication technique described herein to communicate control signalsbetween a dash or console mounted controller and a roof-mounted lightbar. In the example shown, the multi-conductor cable power controlbundle 28 is eliminated as no longer being needed or required. Instead,control signals are communicated via the main power bus that connectsthe battery to the light bar. Additional control signals may becommunicated via the same bus to other devices located at various pointswithin the vehicle. For example, a rear-mounted warning lamp, frontheadlight flashers, etc. may all be controlled via the same controlmechanism and communications path over the main power bus of thevehicle. The cabling shown can be factor-installed single ortwo-conductor power cables, and the data transmitter connection may be atwo-conductor connection to the local power bus as is conventional.

In the FIG. 3 arrangement, a current modulated load 200 is installed ator near the vehicle console and at each of controlled devices (e.g.,light bar 12′, front flashers 16′, rear flashers 18′) there is installeda voltage demodulator 300. FIG. 4 shows an example operation of thecurrent modulated load communications system described herein. Theexample shown is in the context of a vehicle such as a police, emergencyresponse or other vehicle that uses a direct current (DC) power bus, butother environments are also possible. In this particular example, aconventional 12 Volt DC or other lead acid type battery 100 supplies DCpower to the vehicle (although other power sources such as fuel cells,solar cells, capacitive storage cells, or various other DC or AC powersources could be used instead). Battery 100 is recharged by aconventional alternator 102. The “−” terminal of battery 100 isconnected to ground such as a point on the vehicle frame 106 although“+” rail type connections can be used instead.

In the exemplary illustrative non-limiting implementation shown in FIG.4, information to be communicated (“information in”) is applied to acurrent modulated load 200 that is connected to the battery 100's “+”terminal (in a positive-grounded system it could be just as easilyconnected to the “−” terminal). The “information in” controls modulatedload 200 to vary the amount of current the load draws from battery 100.Because battery 100 is capable of delivering only a finite amount ofcurrent (i.e., it is a finite power source with respect to peak ormaximum power delivery and/or amount of current that can be deliveredover time), the loading on the battery due to the current modulated load200 causes the output voltage produced by the battery to vary orfluctuate. The voltage fluctuations that current modulated load 200induces on battery 100's output are responsive to the variations incurrent that the current modulated load 200 draws from the battery.

As shown in the particular illustrative exemplary non-limitingimplementation shown in FIG. 4, if the current modulated load 200 drawscurrent pulses as indicated by the square wave current trace (thepeak-to-peak current is measured in amperes), then the voltagefluctuations induced at the battery 100's “+” output will similarlyexhibit a square wave variation that “tracks” or follows the variablecurrent being drawn by current modulated load 200. One way to thinkabout what is happening is that battery 100 acts as a “mirror” or“repeater” by mirroring or repeating, in its voltage output, thevariations in current being drawn by current modulated load 200. Anotherway to explain it is that by drawing a variable amount of current frombattery 100, current modulated load 200 effectively causes the batteryto modulate its voltage output in a way that is responsive to thevariable current being drawn by the current load 200.

In most conventional vehicles, every electrical device within thevehicle is directly or indirectly connected to the battery 100 as shownin FIG. 5, for example, a variety of different devices including heaterblowers 130, headlights 140, horn 150, taillights, dashboard lights,radios, tape players, power antennas, engine ignition systems andcontrollers, radio location devices, electronic mapping devices, and anyother electrical equipment you can think of may be connected to theoutput of battery 100. Typically, a main power bus connected to thebattery 100's “+” output terminal delivers power to any and allelectrical devices within the entire vehicle. The FIG. 4 exemplaryillustrative non-limiting implementation takes advantage of this powerdistribution throughout the vehicle. More specifically, the voltagefluctuations exhibited at the battery 100's output as shown in FIG. 4will inherently be distributed throughout the vehicle along the variouswiring harnesses and power conductors that are used to power variouson-board electrical devices within the vehicle. Virtually anywhere onthe main power bus, it is possible to observe and detect these voltagefluctuations that current modulated load 200 induces on the battery100's voltage output.

In the FIG. 4 exemplary illustrative non-limiting implementation, avoltage demodulating receiver 300 is placed somewhere (anywhere) on thepower bus or network within the vehicle. For example, voltagedemodulating receiver 300 could be connected to a power connector usedto supply DC power to a roof-mounted light bar. The same or differentvoltage demodulating receiver 300 could be connected to power used tosupply any other device on-board the vehicle. A demodulating receiver300 could be co-located with one current modulated load 200, and anotherco-located demodulated receiver/current modulated load pair could beplaced elsewhere in the vehicle to provide a half-duplex or full duplexpowerline communications system. For example, such a bidirectionalcommunications system could be used to provide positive acknowledgmentof control signaling to ensure information integrity.

In the exemplary illustrative non-limiting implementation shown in FIG.4, voltage demodulating receiver 300 senses the variable voltage presenton the vehicle power bus. Voltage demodulating receiver 300“demodulates” this variable voltage in order to regenerate a facsimileor approximation of the “information in” signal. Voltage demodulatingreceiver 300 provides an “information out” signal that represents suchfacsimile or regeneration. This “information out” signal can be used forany of a variety of different purposes including, for example, control,playback, audio and/or video generation, etc.

The exemplary illustrative non-limiting current modulated load 200 shownin FIG. 4 can use any form of modulation (e.g., frequency modulation,phase modulation, frequency shift keying modulation, amplitudemodulation, pulse width modulation, continuous wave, other) to modulatethe current being drawn by current modulated load 200 in response to the“information in” signal. The particular design of voltage demodulatingreceiver 300 will be generally determined by the type of modulation andthe information encoding used by current modulated load 200.

FIG. 5 shows an example more detailed overall communications system 180using the exemplary non-limiting techniques shown in FIG. 4. In the FIG.5 example shown, current modulated load 200 includes a keypad or otherinput 202 that is provided to a microcontroller 204. The microcontroller204 responds to the user inputs supplied via keypad or other input 202and encodes the resulting user input actions into digital form.

In the particular exemplary illustrative non-limiting implementationshown, the “information in” and “information out” signals can be anytypes of information signals including digital, analog, audio, video,control, intelligence, or any other type of information that needs to beconveyed. In one particular illustrative non-limiting implementation,the “information in” signal could, for example, comprise digital controlsignals used to control the operation of a number of differentelectrical devices within a roof-mounted light bar. As one example, the“information in” signal can be a digitally-encoded bit pattern (4, 8,16, or other bit) digital format where the signals in combination areused to control different light bar devices. An example encoding isshown below in Table 1 for purposes of illustration, but any desiredencoding could be used as those of ordinary skill in the art willrecognize. TABLE I Bit Pattern 0 0 0 0 Reserved 0 0 0 1 Turn on rotator0 0 1 0 Turn off rotator 0 0 1 1 Turn off flasher/strobe 0 1 0 0 Turnoff flasher/strobe 0 1 0 1 Turn on siren 0 1 1 0 Turn off siren 0 1 1 1Turn on alley light(s) 1 0 0 0 Turn off alley light(s) 1 0 0 1 Turn ontakedown lights 1 0 1 0 Turn off takedown lights 1 0 1 1 Turn onpriority green 1 1 0 0 Turn off priority green 1 1 0 1 Aux on 1 1 1 0Aux off 1 1 1 1 Reserved

Referring to FIG. 5 for example, an output of microcontroller 204 isprovided to a field effect transistor (FET) and source resistor or otherswitch controlled load 206. Switch controlled load 206 could, forexample, comprise a specially provided load such as a constant currentload, or it could comprise an existing, substantially resistive loadsuch as for example vehicle headlamps (which could be switched onmomentarily during daylight or switched off momentarily during nighttimeto provide a current loading that is at least in part responsive to themicrocontroller 204's output). The microcontroller 204 output controlsthe switching load 206 to be connected or not connected to the battery100 terminal or in some cases may control the amount of current that theswitch controller load 206 draws from the battery. In the example shown,microcontroller 204 uses a conventional frequency shift keyed (FSK)technique with “marks” and “spaces” to frequency shift key modulate theswitch controlled load 206. This induces an FSK modulated signal on thevoltage produced by battery 100.

As also shown in FIG. 5, the battery 100's output is coupled todemodulating receiver 300 which in this particular exemplaryillustrative non-limiting design includes an FSK demodulator. In moredetail, one exemplary demodulating receiver 300 design may include asignal decoupler 302 which provides an output to an FSK demodulator 304.In that particular implementation, the FSK demodulator 304 provides ademodulated digital output to a microcontroller 306 which decodes theresulting digital signals. As those skilled in the art understand, thesignal decoupler 302, FSK demodulator 304 and microcontroller 306 may,if desired, all be implemented by a digital signalprocessor/microcontroller 308 or other implementations (discrete and/orintegrated) may be used. Load switcher 310 responds to the digitallydecoded control signals to selectively actuate light bar 400 devicessuch as rotators 402, alley lights 404, strobes 406, sirens 408, etc.

FIG. 6 shows an example more detailed schematic block diagram of anillustrative non-limiting exemplary demodulating receiver 300 providingadditional load switching functionality to suppress noise. In theexample shown, load switcher 310 may comprise a variety of discreteswitches that are electrically controlled by the digital output ofmicrocontroller 306 or DSP/microcontroller 308. Such switches mayinclude for example transistors including for example FET's, triacs,relays, solenoids or any other convenient switch design. In the exampleillustrative non-limiting implementation shown, load switching thusoccurs within or in proximity to light bar 400 as opposed to remotelysuch as at a dashboard or console control switch box. Furthermore, it ispossible for microcontroller 306 to temporarily and selectively switchoff noisy electrical loads such as rotators 402 during data reception bydemodulating receiver 300 to reduce the amount of noise present on thepower bus during signal transmission. If such selective switching occursrelatively rapidly (e.g., for 20 ms or less), it will generally beunnoticeable to any observer of the light bar's operation. Suchswitching can occur in synchronism with operation of current modulatedload 200, or it could occur asynchronously (e.g., periodically).

Using load switcher 310 to selectively or fully remove the load from anygiven branch circuit connected to a demodulating receiver 300 serves todramatically increase the branch circuit impedance, such that saidbranch circuit acts as a signal radiator responsive to the voltagemodulation produced by battery 100 instead of a current-carryingconductor supplying power to the load(s) controlled by load switcher300. Those skilled in the art will recognize that the extensivefiltering and demodulating circuitry for receivers located on the samebranch circuit as noise producing loads (e.g.—switching power supplies,flashing lamps, blowers, etc.) is not necessary if those loads aresimply turned off.

Load switcher 310 may be configured intelligently (e.g.—under thecontrol of microcontroller 306) such that non-varying resistive loads,which produce minimal electrical noise, will remain in conduction(e.g.—“on” state), while inductive, capacitive loads, and/or constantlyvarying resistive loads will be interrupted in order to increase thepowerline conducted signal-to-noise ratio so that demodulating receivers(e.g.—signal decoupler 302 and FSK demodulator 304) easily decouple anyvoltage modulation present on the powerline.

A further embodiment of load switcher 310 includes the addition ofcapacitors 900 on the load-side of the switch and/or switches. Thoseskilled in the art will recognize that a properly sized capacitor 900will continue to temporarily supply power to a load or loads for a briefperiod of time if load switcher 310 interrupts power (e.g.—aninexpensive 100,000 microfarad capacitor will easily sustain power torotators 402, which may draw an average of five amperes, for severalmilliseconds, while intelligence is being voltage modulated over thepower bus). A further advantage of this particular enhancement is thereduction of overall noise on the entire electrical bus due to decreasedin-rush current that can be present when a load is fully de-energizedand then is suddenly turned on, particularly if the turning on and offof said load is continuous and frequent.

As also shown in FIG. 6, for example, in one illustrativeimplementation, demodulating receiver 300 may be relatively compact sothat it can be installed within a conventional light bar 400. This meansthat a single positive (or negative) power connection to battery 100 canbe used to both supply power to a light bar 400 and also to supplycontrol signals for controlling operation of the light bar. Use of asingle power conductor of this type eliminates the need to runmulti-conductor power or control cabling to the light bar and also inmany cases may allow the installer to make use of a single powerconductor (or two-conductor, if the positive and ground conductors arerun together) installed at the vehicle factory as the only connectionrequired to both power the light bar and control it.

FIG. 7 shows an exemplary illustrative non-limiting implementation of acontrolled current modulated load circuit 200. In the example shown, amicrocontroller 204 receives input from a keypad 202 or any otherarrangement. In the example shown, keypad 202 may comprise aconventional telephone type keypad allowing an operator to input up tosixteen different types of switch closures. In other implementations,the keypad or other input device 202 may take the form of a conventionalswitchbox of the type shown in FIG. 1A including for example a slider orprogressive switch and a number of discrete ON/OFF toggle switches. Theoutputs of keypad or other input device 202 are provided to the inputsof controller 204. Controller 204 may provide local indicator lightssuch as shown generally at 220, 222 (an additional LCD or other displaymay also be provided if desired). In addition, a gate control signal222, which may be post width modulated, is provided at an output ofcontroller 204. This gate control signal 222 is applied to the gate of afield effect transistor (FET) 206 operating in the enhancement mode. Thecontroller may selectively switch-connect an additional FSK oscillator(e.g., with an output frequency in the range of 11.5 KHz to 12.5 KHz) tothe FET gate input, or such FSK oscillation generation may be providedby the controller under software control.

In one example illustrative non-limiting implementation, acurrent-modulated load can be a N-channel MOSFET operating in theenhancement mode. The FET source is connected through a resistor toground. The FET drain is connected to the positive powerline rail. Aconstant current may be drawn through this arrangement that is dependenton (1) the voltage applied to the FET gate, and (2) the value of theFET's source resistor, while independent of the voltage present on thepositive powerline rail.

A FET operating in the enhancement mode for the purpose of drawing aconstant current is well known in the art. However, in the illustrativeexemplary non-limiting implementation herein, the FET is modulated forthe purpose of communicating signaling across the vehicle's electricalsystem as will be described.

Most vehicles contain electrical systems which, at their core, arepowered by batteries that are recharged by alternators. All batterieshave maximum delivery capacities, and are usually rated in ampere-hours.Lead-acid batteries—the type most commonly found in vehicles-exhibit anopen circuit voltage that instantly decreases when a load is applied.This voltage drop (as measured from the open circuit voltage) isdependent upon the relative charge of the battery and the total loadapplied.

If the FET is modulated such that a constant current is drawn on a givenfrequency and duty cycle from the electrical system power system'sbattery, the battery's output voltage will be current modulated suchthat the resulting voltage waveform will reflect the load applied. Forexample, if a FET were driven in the enhancement mode such that itproduces a square wave frequency of 10 kHz at a duty cycle of 50% whenthe current drawn by the FET in conduction is 5.0 amperes and the powersource is a lead acid battery (with or without the associated alternatoroperating in the charging mode), it can be observed that, depending uponthe level of charge existing on the battery (and whether or not thealternator is charging the same), and assuming that there are no otherconnected loads, the measured peak-to-peak voltage of the resultingbattery voltage can vary from as little as 40 millivolts to as much as500 millivolts for an average vehicle battery. This voltage variation,which is present throughout the entire electrical system regardless ofswitching on and off of the loads, can be easily detected anddemodulated without complex filtering and/or sophisticated demodulatingcircuitry. Those skilled in the art will recognize that the actualamplitude of the voltage modulation produced by the battery will beinfluenced by other loads connected to the vehicle's power bus.Modulation of the N-channel MOSFET operating in the enhancement mode, orany switch that draws a predictable or unpredictable current at a givenfrequency, will cause a finite (or limited) power source (e.g., a leadacid battery) to become a “radiator” of a resulting current-modulatedsignal that is represented as a “voltage mirror” of the transmitteritself. Thus, the finite power source becomes a transmitter “repeater”that produces a similar, if not identical, voltage signal on eachelectrically connected node of the system.

Powerline carrier receivers that are in line with heavy current loadsalso producing lots of conducted noise typically use extensive filteringin order for any reliable signal data to be extracted. If the noiseproduced is also a by-product of numerous loads constantly turning onand off (e.g., an emergency vehicle light bar), then the problem isfurther exacerbated. As is well-known, generally the best receiver forany type of signal is an antenna. The very nature of most antennas isthat they are usually resonant at or near a desired frequency ofinterest, that the overall line impedance is relatively high, and thedesired frequency sought (or to be tuned) is effectively coupled to agiven receiver. In the exemplary illustrative non-limitingimplementation, a single wire that performs as an antenna and highcurrent conductor is used to decouple a power line carrier signal andstill be capable of delivering power to a given load.

One characteristic of a MOSFET is its inherent ability to switch loadsrapidly on and off. What was once accomplished with large mechanicalrelays that occupied rather large mounting footprints can now be handledinexpensively with a small FET that is also capable of switching tens ofamperes of current. An FET (or any other high speed current switchingdevice) may be used to isolate the load on a single current-carryingconductor such that the conductor changes rapidly from a low to highimpedance state during which time a power line carrier signal can beeffectively decoupled from the same conductor which, in its highimpedance state, more closely resembles an antenna. On a singleconductor (e.g., the 12 VDC cable connected to a light bar), between theload and power source is a receiver and a FET switch. The FET is locatedbetween the receiver and the load and hence, by proximity andelectrically, the receiver would be in closest proximity to the powersource. At a given point in time (e.g., predetermined in advance and/orsynchronized to a received signal and/or asynchronously), the FET opens(i.e., disconnects the load) such that the conductor's impedance changesfrom low to high. This increases the signal-to-noise ratio thatpreviously existed (while the FET was in conduction) and thereforepermits a direct-coupled receiver to more easily extract a data signalfrom the power line.

FIG. 8A shows an example more detailed illustrative non-limitingimplementation of a demodulating receiver 300. In the example shown, theconnection from battery 100 may be filtered with a conventional tankcircuit 302 and then filtered by a conventional bandpass filter 330. Anynumber of bandpass filter stages 332 may be used to provide a two-stage,three-stage, four-stage or any desired type of bandpass filter. Thedecoupler 302 in filtering is generally used to eliminate noise. It iswell known that many of the electrical devices operating within avehicle generate substantial amounts of wide-band noise. The ignitionsystem typically produces significant radiated and conducted noisebecause it generates sparks and has a variety of switch closures andopenings. Any device with a motor (e.g., a heater blower, an airconditioner fan, a light bar rotator, etc.) may all also generatesubstantial amounts of electrical noise and place such noise on thevehicle's main power bus. The signal decoupler 302 filters out as muchof this noise as possible while passing the desired information-varyingsignal onto an FSK demodulator 304 in the form in this particularillustrative non-limiting implementation of a phase lock loop 340. Aswill be understood by those of ordinary skill in the art, the currentmodulated load controller 204 is preferably designed to provide aparticular known frequency output to FET 206 so that afrequency-selective signal decoupler may be used to providefrequency-selective noise rejection (i.e., only pass a particular narrowfrequency range of frequencies while rejecting noise at otherfrequencies). Such techniques are well known to radio operatorsattempting to copy Morse Code or other intelligence on a noisy frequencyband such as during mid-summer electrical storms.

In the exemplary arrangement shown in FIG. 8A, phase lock loop 340comprises a conventional phase lock loop integrated circuit that locksonto the FSK frequency and detects the presence of “mark” and “space”FSK modulation-producing a data output on line 342. Such data output maybe used to control indicator light 344 and is also provided in theillustrative exemplary non-limiting implementation shown to the input ofa microprocessor 306 shown in FIG. 8B. Microprocessor 306 decodes theresulting digital output and provides decoded control signals to MOSFETor other drivers 350. These driver circuits may drive FET or otherelectronic switches 352 to control on/off power to a number of loadssuch as rotators 402, alley lights 404, strobes 406, siren 408, prioritygreen transmitters 410, or any other electrical or electronic deviceimaginable.

FIG. 9 shows an exemplary illustrative non-limiting flowchart of programcontrol steps that the controlled current modulated load controller 204may perform. FIG. 9 illustrates one possible communications method—inthis case frequency shift keying (FSK) at the load to produce a pulsewidth modulated (PWM) data stream at the receiver. The controller 204may, for example, periodically poll the keypad or other input device 202or may respond to service and input interrupt (block 502) as thoseskilled in the art understand. If a keypad input or interrupt isdetected (“yes” exit to decision block 504), the controller 204determines pulse width modulated timing and/or duration (block 506) andthen may execute an appropriate number of cycles of FSK load modulation(block 508).

This particular example illustrative non-limiting implementation assumesthat a given keypad entry will produce a 50% duty cycle pulse width withmark and space times of (x) ms (see FIG. 10 timing diagram) for (y)duration (# of cycles). The controller 204 may then modulate the load206 at an FSK mark frequency F₁ for the desired duration (block 510). Itmay also then modulate the load at the FSK space frequency F₂ for adesired duration (block 512). It may repeat these steps for a desirednumber of FSK modulation cycles (“no” exit to decision block 514) beforereturning to poll or otherwise service the input device 202 (“yes” exitto decision block 514).

FIG. 10 shows an exemplary illustrative non-limiting flowchart ofprogram control steps for the receiver microcontroller 306. In thisparticular example shown, the receiver microcontroller 206 performs apolling routing to determine whether the FSK demodulator 304 hasachieved a lock (e.g., based on the FSK_LOCK output from thedemodulator) (block 552). Once FSK lock has been detected (“yes” exit todecision block 554), then the microcontroller 306 measures high and/orlow data out pulse width on FSK demodulator 304's data out line (block556). This latter operation distinguishes between noise spikes andintelligence bearing signals in the exemplary illustrativeimplementation by requiring information-bearing pulses to have a certainduration that is greater than most noise spikes (e.g., 3 ms) but lessthan voltage changes induced by activation of a typical vehicular device(e.g., 10 ms) (decision block 558). If no valid pulse is detected (“no”exit to decision block 558), then microcontroller 306 determines whetherthis a “first” exception during this particular FSK lock operation(decision block 560). If this is not the first exception (“no” exit todecision block 560), then counters are reset (block 562) and controlreturns to the FSK lock polling routine (block 552). If the pulsereceived is not a valid pulse and this is the first exception during thecurrent FSK lock operation (“yes” exit to decision block 560), thencontrol returns to re-measuring the high and/or low data out pulse width(block 556).

If, on the other hand, decision block 558 detects a valid informationpulse (“yes” exit to decision block 558; block 560), thenmicrocontroller 306 determines the pulse duration which, in oneexemplary implementation, determines the control of a specific I/Odevice (block 562). For example, in one exemplary illustrativenon-limiting implementation, a pulse duration of 4 ms may provide onetype of I/O whereas a pulse duration of 7 ms may determine another typeof I/O. In the exemplary illustrative non-limiting implementation shown,microcontroller 306 facilitates the type of I/O control required (block564) and then control returns to block 552.

FIG. 11 shows some example illustrative waveforms that may be presentwithin the exemplary illustrative non-limiting implementation shown inFIGS. 7, 8A and 8B. In this particular exemplary illustrativenon-limiting implementation, the keypad input on the top line is decodedas “send 4 pulses, f1=5 ms (mark, high), f2=5 ms (space, low). Ofcourse, other modulation durations, schemes and/or arrangements are alsopossible. Note that the bottom line in the diagram exhibits a slight PLLresponse delay on FSK data after data_locked is enabled.

All sources and other items cited above are hereby incorporated byreference into this patent specification as if expressly set forthherein.

While the technology herein has been described in connection withexemplary illustrative non-limiting embodiments, the invention is not tobe limited by the disclosure. For example, while illustrativenon-limiting exemplary implementations described herein relate tocontrolling visible and/or audible warning systems for emergencyresponse motor vehicles, the technology herein is not limited to thoseparticular applications or environments. For example, the technologyherein could be used on different types of vehicles including trains,airplanes, buses, boats, spacecraft, or any other type of vehicle. Thetechnology herein could be used to control devices and equipment otherthan warning devices, including for example ignition and enginemanagement systems, entertainment systems, navigation equipment, driveror passenger comfort and/or convenience equipment, vehicle networkingand/or integration, or any other type of equipment that can be used onboard a vehicle. Furthermore, the technology herein is not limited tocontrol of devices on vehicles, but rather than be used in any contextwhatsoever wherein it is desirable to communicate information of anytype over a powerline. While the illustrative non-limiting exemplaryimplementations herein relate to DC powerline applications, otherpowerline applications (e.g, AC, other) could be used. The invention isintended to be defined by the claims and to cover all corresponding andequivalent arrangements whether or not specifically disclosed herein.

1. A vehicular based system for providing controllable audible and/orvisible warning indications that a law enforcement and/or rescueemergency exists, said system comprising: a current modulator; a batterycoupled to said current modulator, said battery providing an outputvoltage that is at least in part responsive to said current modulator;and a voltage demodulator coupled to said battery, said voltagedemodulator demodulating said battery output voltage and outputtingresponsive control signals, and a light display unit responsive to saidcontrol signals, said light display unit comprising a light and soundbar mounted to the exterior roof of said vehicle.
 2. A communicationskit for controlling a vehicular based system for providing controllableaudible and/or visible warning indications that a law enforcement and/orrescue emergency exists, said system including a battery and a lightdisplay unit comprising a light and sound bar mounted to the exteriorroof of said vehicle, said kit comprising: a current modulator adaptedfor coupling to said battery, said current modulator, in use, causingsaid battery to generate an output voltage that is at least in partresponsive to said current modulator; and a voltage demodulator coupledto said battery, said voltage demodulator demodulating said batteryoutput voltage and outputting responsive control signals to control saidlight display unit.
 3. The kit as in claim 2 wherein said currentmodulator and voltage demodulator are disposed within a common housing.4. The kit of claim 2 wherein said current modulator includes a FET inenhancement mode.
 5. The kit of claim 2 wherein said current modulatorprovides pulse width modulation.
 6. The kit of claim 2 wherein saidvoltage demodulator is adapted to be installed within said light displayunit.
 7. The kit of claim 6 wherein said light display unit comprises aroof-mounted light bar.
 8. A system for using a power source connectedto a power line to communicate information to a device coupled to saidpower line, said system comprising: a modulated current load coupled tosaid power line, said modulated current load drawing a current from saidpower line that is at least in part responsive to an information signal,said drawn current inducing voltage fluctuations at said power sourcethat are in response to said information signal; and a device coupled tosaid power line, said device capturing said voltage fluctuations on saidpower line and demodulating said captured voltage fluctuations torecover said information signal.
 9. The system of claim 8 wherein saidpower source comprises a finite power source.
 10. The system of claim 8wherein said power source comprises a direct current batter.
 11. Thesystem of claim 8 further including a noise interrupter coupled to saidpower line, said noise interrupter temporarily disconnecting a noisyload from said power line during capture of said voltage fluctuations bysaid device.
 12. A system for communicating information over a powerline, comprising: means responsive to an information signal and coupledto said power line for drawing a current from said power line that is atleast in part substantially instantaneously responsive to saidinformation signal, said drawn current inducing voltage fluctuations onsaid power line that are at least in part instantaneously responsive tosaid drawn current; and means coupled to said power line for capturingand demodulating said voltage fluctuations to extract at least a portionof said information signal.
 13. A system for using a power sourceconnected to a power line to communicate information to a device coupledto said power line, said system comprising: a data transmitter thatinduces fluctuations on said power line in response to said informationsignal; a data receiver coupled to said power line, said data receivercapturing said fluctuations on said power line and performing at leastaction in response thereto; and a load interrupter coupled to said datareceiver, said load interrupter temporarily decouples at least one loadfrom said power line during said capturing of fluctuations.
 14. Thesystem of claim 13 further including a charge storing element coupled tosaid load interrupter, said charge storing element supplying power tosaid at least one load while said load interrupter temporarily decouplessaid at least one load from said power line.
 15. The system of claim 14wherein said charge storing element comprises at least one capacitor.16. On a vehicle based system for providing controllable audible and/orvisible warning indications that a law enforcement and/or rescueemergency exists, said system comprising: a data transmitter connectedto said powerline, said data transmitter inserting a control signal ontosaid powerline; a data receiver connected to said powerline, said datareceiver obtaining said control signal from said powerline; and a lightbar control unit coupled to said data receiver, said light bar controlunit controlling light and sound emanating from the exterior roof ofsaid vehicle at least in part in response to said obtained controlsignal.
 17. A light bar of the type for mounting on the exterior roof ofa law enforcement and/or rescue vehicle, said light bar comprising: apower connector; at least one rotator; a data receiver coupled to saidpower connector, said data receiver receiving control signals from saidpower connector; and a controller that selectively applies power to saidrotator at least in part in response to said received control signals,said controller momentarily interrupting power to said rotator duringcontrol signal reception by said data receiver.